Voltage converter applying an antiskid logic element

ABSTRACT

A voltage converter set designed to feed an antiskid logic element and to modify the wheel speed sensor signals. The converter set includes a proportional converter and an inversely proportional converter, connected through a diode, so that the output voltage of the converter set is higher for the low wheel speeds. The invention also provides the combination of several converter sets with a single antiskid logic element in a circuit of the exclusive &#39;&#39;&#39;&#39;OR&#39;&#39;&#39;&#39; or &#39;&#39;&#39;&#39;SELECT LOW&#39;&#39;&#39;&#39; type.

United States Patent 1191 Marouby Jan. 1, 1974 [5 VOLTAGE CONVERTERAPPLYING AN 3,642,329 2/1972 Zechnall et a1. 303/21 BE ANTISKID LOGICELEMENT 3,614,634 10/1971 Jones et al. 307/233 X 3,584,298 6/1971Kolbiaz 307/233 X Inventor: y Marouby, y, France 3,535,004 10/1970Howard 6:211. 303 21 EB [73] Assignee: Societe Anonyme D.B.A., Clichy,

France Primary ExaminerDuane A. Reger Assistant Examiner-Stephen G.Kunin [22] Flled' 1972 Att0rneyl(en C. Decker et a1. [21] Appl. No.:245,333

[57] ABSTRACT [30] Foreign Apphcatlon Pnonty Data A voltage converterset designed to feed an antiskid May 4, 1971 France 7ll596l logicelement and to modify the wheel Speed Sensor si als. [52] US. Cl 303/21R, 307/233, 307/261, gn

3O7/295 328/127, 328/140 The converter set lncludes a proportionalconverter [51] Int. Cl B60t 8/00 and a inversely proportional converterconnected [58] Field of Search l88/l8l- 303/20 through a dime that theOutput vltage 0f the 30301. 307/233 261 324/16|, l62 converter set ishigher for the low wheel speeds, The 328/24 127 3 2 3740/52 R inventionalso provides the combination of several y converter sets with a singleantiskid logic element in a [56] References Cited circuit of theexclusive OR or SELECT LOW" UNITED STATES PATENTS type" 3,652,134 3/l972Hiscox 303/21 CG 4 Claims, 6 Drawing Figures VOLTAGE CONVERTER APPLYINGAN ANTISKID LOGIC ELEMENT The invention relates essentially to a voltageconverter set designed to feed an anti-skid logic element and to deliverto this element a voltage representing the speed of rotation of a wheelafter the conversion of electrical signals from a sensor/amplifier unit.

The converter set in accordance with the invention is designed to besituated between at least one electric generator associated with avehicle wheel and the input of an electronic logic element of ananti-skid circuit controlling the application or release of the brakingmeans-of the vehicle and comprising at least one proportional convertersituated between the output of the generator and the input of the saidlogic element in order to supply the latter with a direct-currentvoltage of given polarity proportional to the speed of rotation of thewheel. lt is characterised in that it also comprises another converterof the inversely proportional type associated with the proportionalconverter and having an input connected to the generator and an outputconnected by a diode or the like provided at the input of the logicelement so that the said other converter applies to the logic element adirect-current voltage inversely proportional to the speed of rotationof the wheel when this voltage is greater than the voltage supplied bythe proportional converter.

According to another feature of the invention, the voltage across theterminals of the proportional converter becomes zero at a low speed ofrotation of the wheel associated with the generator and the voltageacross the terminals of the inversely proportional converter is zero atsubstantially the same speed whereas it increases with decreasing speedbelow the said low speed, the voltage across the terminals of theproportional converter then being zero.

According to a further feature of the invention, the voltage across theterminals of the inversely proportional converter increases much fasterwith decreasing wheel speed below the said low speed than the voltageacross the terminals of the proportional converter increases withincreasing wheel speed above the said low speed.

Known electric braking systems have a proportional converter situatedbetween the sensor/amplifier unit and the input of the anti-skid logicelement. When the rotational speed of the wheel controlled is close tozero, therefore, the voltage delivered by the converter to the logicelement is almost zero, and since stray voltages superimpose themselveson the substantially zero voltage it is difficult to use this referenceto control the electronic system. The electronic system then fails andno longer knows whether the hydraulic braking pressure must be relaxedor reapplied when the vehicle stops.

A converter set embodying the invention, as defined above, enables thisdisadvantage to be overcome. If the set with only a proportionalconverter is combined with a converter of the inversely proportionaltype whose input is connected to the sensor/amplifier unit and whoseoutput is connected by a suitably poled diode to the input of the logicelement, the said converter set supplies the logic element at speedsclose to zero with voltages slightly greater than the stray voltageswhich the logic element can use. Also, the voltages applied to the logicelement increase rapidly with slowly decreasing speed until the speeddrops to zero, and the logic element receives increasing voltagessimulating an increase in the wheel speed although the wheel is slowingdown, at a low speed, with the result that the brake associated with thewheel can be operated hydraulically until the wheel has come to a stop.

An additional advantage can be obtained if, in accordance with anotherfeature of the invention, the converter set comprises a plurality ofgroups of proportional and inversely proportional converters connectedtogether in pairs by a diode and connected respectively to electricgenerators, one group per wheel controlled, the said groups beingconnected to the (single) logic element by means of a conventionalcircuit of the SE- LECT LOW type. The additional advantage lies in thefact that, in the case of a device embodying the invention, when onewheel is locked the corresponding voltage applied to the SELECT LOW"circuit is high, and the logic element is then controlled by a wheelwhich is running at a low speed but is still rotating, that is to say,supplying a lower voltage than that corresponding to the locked wheel.As will be explained in more detail in the following description, theelectronic device not only prevents locking of a wheel threatening tolock, but also permits a wheel already locked to be set in motion againif there is a logic element and hydraulic system common to all thewheels.

The invention will be better understood from the following descriptionreferring to the accompanying drawings, in which FIG. 1 represents aconverter set embodying the invention, associated with asensor/amplifier unit and with an anti-skid logic element,

FIG. 2 represents the response curve for the set illustrated in FIG. 1,

FIG. 3 represents a converter set embodying the invention with aplurality of converter groups connected to the input of ananti-skid'logic element by a circuit of the exclusive OR" type, and

FIGS. 4 to 6 show curves similar to those in FIG. 2, with variousoperating points for a plurality of wheels which control the anti-skidlogic element.

FIG. I is a diagram of an electronic anti-skid control circuit embodyingthe invention, 'with a sensor S in front of which a toothed disc Dattached to the wheel of a vehicle rotates, and which feeds a signal toan amplifier A. After amplification the signal is applied to a groupcomprising a proportional frequency-t0- voltage converter P and aninversely proportional frequency-to-voltage" converter IP at the inputof a conventional anti-skid logic element L. A diode R is insertedbetween the converter IP and the logic element L before the point atwhich the converter P is connected to the logic element. The diode R ispoled so that voltages from the converter IP greater than those from theconverter P are applied to the logic element. The output of the logicelement is connected to a hydraulic system (not shown), to which itfeeds admission or shut-off signals to apply or release the brake of thevehicle wheel monitored by the sensor S.

The electronic circuits of the frequency-to-voltage P and IP convertersshown in FIG. 1 will now be described.

The converter P has an input capacitor 10 connected both to theamplifier A and to the emitter of a PNP transistor 12 whose base isconnected to the higher tension, the collector being connected by way ofa varaible resistor 14 to earth, which is at the lower tension. A diode16 is provided between the base of the transistor 12 and its emitter.This diode 16 is conductive in respect of negative voltages. Thecollector of the transistor 12 is connected to the higher tension by acapacitor 18 and to the lower tension by an assembly comprising acapacitor 20 and resistor 22 in series, this assembly being mounted inparallel with the variable resistor 14. The output of the converter Pappears at a point 21 between the resistor 22 and the capacitor 20. Thecapacitors 18 and 20 and resistor 22 are selected to give the desiredresponse time 'for the converter.

The inversely proportional converter IP has an input capacitor 24connected both to the amplifier A and, by a diode 26 and a filtercomprising a resistor 28 and capacitors 30 and 32, to a NPN transistor36. The emitter of this transistor is connected directly to earth, whichis at negative high tension, and its collector is connected by aresistor 38 to the positive high tension. A point 40 between thecollector of the transistor 36 and the resistor 38 forms one outputterminal of the converter IP, the other output terminal being the earth.The output 40 is connected to the output 21 of the converter P by adiode R or similar element conductive in the direction away from 40 andtowards 21. The set comprising P, I? and R therefore has two outputterminals the higher tension, and the connecting point 42 to which thelines from the terminal 21 and from the diode R lead. This point 42 isconnected to the input of the logic element L.

The set shown in FIG. 1 operates as follows. It delivers to the logicelement L a voltage V, dependent on the speed of the wheel associatedwith the sensor S and shown on the curve in FIG. 2. The converter Pprovides a voltage proportional to the speed of rotation of the wheeland represented by the curve branch P when this speed is between themaximum speed of the vehicle and a low speed w of the order of 2 km/h,at which the voltage V becomes zero. From this value w, the converter lPsupplies a voltage inversely proportional to the speed and increasingwith decreasing speed below w. It will be appreciated that beyond thepoint w, as mentioned in the preamble, the logic element receivesinformation in the form of voltages increasing with decreasing speed andbehaves as if the wheel were accelerating, with the result that itpermits free operation of the braking means without interfering withthem.

Again as already stated, an even more useful result is obtained if theset of converters associated with the logic element includes a pluralityof groups of converters, each group comprising a proportional and an inversely proportional converter and a diode connected to the logicelement by a SELECT LOW or exclusive "OR" circuit.

An arrangement of this kind is shown in FIG. 3. Amplifiers A1, A2.. An(FIG. 3 associated with respective sensors and wheels (not shown) applyto converter/diode groups P1, IPl, R1 P2, 1P2, R2; Pn, IPn, Rn positivedirect-current pulses at the diodes D1, D2 Dr: of a known SELECT LOWcircuit SL. The latter comprises a PNP transistor T of which the base isconnected to the various diodes D1, D2 Dn, the collector to earth andthe emitter both to the input of the logic element and, by way of asuitable resistor, to the higher tension.

As just described, the circuit shown in FIG. 3 feeds to the logicelement L the lowest of the voltages applied to the diodes D1, D2, Dn.The voltages applied to these diodes are proportional to the speed ofrotation of the wheel concerned and are of the type illustrated on thecurve in FIG. 2. The positive direct-current voltage fed by thetransistor T to the logic element L will therefore be a voltage whichmay equally well lie on either branch P or IP of the curve for theassociated wheel and which will be the lowest of the voltages applied tothe circuit SL. In fact the circuit SL will generally feed the logicelement L with voltages situated on the branch P, since with a low andgradually decreasing wheel speed below w the voltage will rise rapdilywhen a given wheel is close to locking and therefore only the voltagesfor operating points situated on branch P will be taken into account.This arrangmenet naturally has an advantage over the device having onlya proportional converter to feed each diode, in which the SL circuitceased to give any information concerning moving wheels once the speedof one wheel has reached zero.

FIGS. 4 to 6 represent the superimposed curves V f(W), assumed to beidentical, for the four wheels of a vehicle. Small circles indicate theoperating points for the various speeds and voltages of these fourwheels. It should be noted that the curves V f (W) might of course bedifferent for the different axles, giving different w values for thevarious axles. In FIG. 4 the four operating points 1 to 4 for thevarious wheels are situated on branch P. In this case all the wheels areturning. Wheel 1 is turning at the lowest speed, and it is the voltagefrom this wheels converter set which will be applied to the logicelement L by the circuit SL. On receiving this information the logicelement L will send signals to the hydraulic system operating the brakesafter analyzing the deceleration conditions for the wheel whoseoperating point is 1.

FIG. 5 illustrates a case in which the anti-skid system has not operatedsufficiently effectively and the wheel whose operating point is 1 hascontinued to slow down and has reached a speed lower than the speed w.As FIG. 5 shows the other wheels (points 2 to 4) have also slowed down,and the logic element L will now be controlled by the wheel representedby point 2. If the deceleration of the latter wheel is consideredexcessive by the logic element, this element will order the hydraulicsystem to release the brakes. All the wheels, including wheel 1, willbenefit from this order, and the point 1 will return to branch P as inFIG. 4.

In FIG. 6 all the operating points 1 to 4 are on branch IP of thecharacteristic curve. This may occur by chance or after braking suitablycontrolled by the antiskid device. The logic element L receivesinformation corresponding to the lowest voltage, that is, to point 4,and during further deceleration of the vehicle it interprets theinformation received as acceleration because the voltage V is rising. Asa result the logic element does not send any signal interfering withbraking, and the driver can stop the vehicle as if the anti-skid devicedid not exist.

I claim 1. In a vehicle having a wheel and a brake controlling saidwheel, an adaptive braking system for controlling said brake comprising:

first means for generating a first signal directly proportioned to therotational velocity of said wheel;

second means for generating a second signal inversely proportional tothe rotational velocity of said wheel; logic means having an outputterminal, and an input terminal operatively connected to said first andsecond means for receiving said first and second signals, said logicmeans being responsive to the signal transmitted to the input terminalfor sensing an incipient skidding condition of said wheel and generatinga signal at said output terminal for relieving braking pressure in saidbrake; and means inhibiting said second signal when the value of saidfirst signal is greater than the value of said second signal butpermitting transmission of said second signal to said input terminalwhen the value of said second signal is greater than the value of saidfirst signal. 2. The invention of claim 1, wherein said first meansgenerates a first signal having a value of zero at a relatively lowwheel rotational velocity and said second means generates a secondsignal having a value of zero at substantially the same relatively lowwheel rotational value that the first signal has a value of zero.

3. The invention of claim 2, wherein said second means increases thevalue of said second signal at a greater rate when the rotationalvelocity of said wheel decreases below said relatively low velocity thanthe rate at which said first means increases the value of said firstsignal as the rotational velocity is increased above said relatively lowrotational velocity of said wheel.

4. The invention of claim 1, wherein said vehicle has a plurality ofwheels with corresponding brakes controlling the wheels andcorresponding first means, second means, and inhibiting means for eachof said wheels, theoutput of each of said inhibiting means having acommon connection with the output of a corresponding first means, eachof said common connections being connected to the input terminal of saidlogic means through a diode.

1. In a vehicle having a wheel and a brake controlling said wheel, anadaptive braking system for controlling said brake comprising: firstmeans for generating a first signal directly proportioned to therotational velocity of said wheel; second means for generating a secondsignal inversely proportional to the rotational velocity of said wheel;logic means having an output terminal, and an input terminal operativelyconnected to said first and second means for receiving said first andsecond signals, said logic means being responsive to the signaltransmitted to the input terminal for sensing an incipient skiddingcondition of said wheel and generating a signal at said output terminalfor relieving braking pressure in said brake; and means inhibiting saidsecond signal when the value of said first signal is greater than thevalue of said second signal but permitting transmission of said secondsignal to said input terminal when the value of said second signal isgreater than the value of said first sigNal.
 2. The invention of claim1, wherein said first means generates a first signal having a value ofzero at a relatively low wheel rotational velocity and said second meansgenerates a second signal having a value of zero at substantially thesame relatively low wheel rotational value that the first signal has avalue of zero.
 3. The invention of claim 2, wherein said second meansincreases the value of said second signal at a greater rate when therotational velocity of said wheel decreases below said relatively lowvelocity than the rate at which said first means increases the value ofsaid first signal as the rotational velocity is increased above saidrelatively low rotational velocity of said wheel.
 4. The invention ofclaim 1, wherein said vehicle has a plurality of wheels withcorresponding brakes controlling the wheels and corresponding firstmeans, second means, and inhibiting means for each of said wheels, theoutput of each of said inhibiting means having a common connection withthe output of a corresponding first means, each of said commonconnections being connected to the input terminal of said logic meansthrough a diode.